I tried all the research I can from YouTube and Google but still I was not been able to make the port forward work for my Hikvision DVR.

I attached a full detailed diagram from my setup.

I open the ports of 8081 as HTTP port, 8000 as Server port, and 554 for RSTP from my local router pointing to my DVR IP address 192.168.100.64.
From my main router connected to the internet I add dstnat 192.168.100.240 port 8081 to my local routers ip.

What am I missing here?

Thank you very much

Your diagram didn't make it here.

One quick option is to enable uPnP on the router and NVR. That should open the need ports. Since uPnP will generate dynamic firewall NAT rules, you can use those as examples to create your own [static] rules & disable uPnP later.